1. Field of the Invention
The present invention relates to an ignition apparatus for an internal combustion engine in which a spark plug receives high voltage for ignition generated from a secondary winding of an ignition coil upon intermittent supply of primary current to a primary winding thereof, such that the spark plug produces spark discharge in order to burn a fuel-air mixture.
2. Description of the Related Art
Spark energy which an internal combustion engine requires for proper burning of a fuel-air mixture has been known to change depending not only on the type of internal combustion engine, but also on operation conditions such as engine speed and engine load. Spark energy can be represented by the product of the magnitude of discharge current flowing as a result of spark discharge and the duration of the spark discharge.
For example, during low-speed, light-load operation such as idling operation, the amount of fuel-air mixture charged into a combustion chamber is small, and the speed of turbulent flow (swirl flow or tumble flow) of the fuel-air mixture is low. Consequently, combustion of the fuel-air mixture proceeds very slowly. Accordingly, in order to attain stable combustion during low-speed, light-load operation, spark energy must be increased to thereby promote combustion of the fuel-air mixture. Meanwhile, during high-speed, heavy-load operation, the density of the fuel-air mixture charged into the combustion chamber increases, and the speed of turbulent flow of the fuel-air mixture is high, so that the fuel is uniformly agitated. Therefore, sufficient combustion can be attained by means of relatively low spark energy.
In addition, the requisite spark energy varies depending on the air-fuel ratio of the fuel-air mixture. For example, when an internal combustion engine is operated with a lean fuel-air mixture having an air-fuel ratio of 20 or more as in the case of a lean burn engine, the density of fuel is low, and consequently the fuel-air mixture has low ignitability. Therefore, the spark energy must be increased.
In view of the foregoing, a conventional ignition apparatus for an internal combustion engine is designed such that insufficient spark energy does not arise; i.e., the ignition apparatus supplies the maximum spark energy required under various operation conditions of the internal combustion engine.
3. Problems Solved by the Invention
However, the above-described conventional ignition apparatus has the following drawbacks. In a state in which an internal combustion engine can be operated by spark energy lower than the maximum spark energy (e.g., during high-speed, heavy-load operation), supply of spark energy becomes excessive, and the excessive spark energy does not improve the ignitability but accelerates consumption of the spark plug electrodes. In addition, when the internal combustion engine is operated at higher speed or under a heavier load, or at high air-fuel ratio, the speed of turbulent flow of fuel-air mixture increases, and thus, a so-called multiple discharge phenomenon occurs easily. That is, in such a state, spark is caused to flow toward the downstream side during a second half of the spark discharge in which spark energy decreases, the spark discharge is then interrupted, and another spark discharge is generated again. In this manner, multiple discharge occurs. When such a phenomenon occurs, spark concentrates at a downstream point, and electrode temperature increases sharply, thereby accelerating sputtering or melting of electrodes of the spark plug, and only downstream portions of the electrodes are consumed; i.e., so-called local consumption occurs, resulting in shortened service life of the spark plug.
Meanwhile, in recent years, a so-called full-transistor igniter has been widely used for an internal combustion engine. In the full-transistor igniter, a semiconductor device such as a power transistor is used as a switching element for intermittently supplying electricity to a primary winding of an ignition coil in order to apply high voltage for ignition to a spark plug. In such a full-transistor igniter, since the duration of supply of electricity to the primary winding before spark discharge (ignition timing) is controlled (i.e., the drive duration of the switching element is controlled) in accordance with operation conditions of the internal combustion engine, the amount of magnetic flux energy which is accumulated in the ignition coil to be used as spark discharge can be controlled to a level required for combustion of the fuel-air mixture.
However, when the duration of supply of electricity to the primary winding before spark discharge is shortened, the amount of magnetic flux energy which is accumulated in the ignition coil decreases, and consequently the high voltage for ignition generated at the secondary winding through intermittent supply of primary current decreases accordingly. As a result, when electricity-supply duration is controlled in the above-described manner, and the internal combustion engine is operated under conditions, such as high-speed, heavy-load conditions, in which high voltage is required for generation of spark discharge although only a relatively small amount of spark energy is required, the high voltage for ignition generated at the secondary winding decreases and misfire may occur.
In view of the foregoing, as shown in Japanese Patent Application Laid-Open (kokai) No. 11-41717, the present inventors proposed an ignition apparatus for an internal combustion engine which, instead of controlling the duration of supply of electricity to the primary winding of an ignition coil before spark discharge, resumes supply of electricity to the primary winding during spark discharge by use of spark-discharge interruption switching means, to thereby stop spark discharge. When this ignition apparatus for an internal combustion engine is used, it becomes possible to interrupt spark discharge after elapse of a spark discharge duration suitable for operation conditions of the internal combustion engine, while maintaining high voltage for ignition generated at the secondary winding through intermittent supply of electricity to the primary winding. In this manner, the amount of spark energy can be controlled to a proper level.
If the primary current flows continuously after supply of the primary current is resumed for the purpose of interrupting spark discharge, the amount of heat generated by the spark-discharge interruption switching means increases, and power is needlessly consumed. Therefore, the supply of electricity is desirably stopped at a proper timing. However, if the primary current flowing after resumption of electricity supply is stopped abruptly, spark discharge is generated again, thereby impairing operation of the internal combustion engine.
In view of the foregoing, in the ignition apparatus disclosed in Japanese Patent Application Laid-Open No. 11-41717, a capacitive element such as a capacitor is connected in series to the spark-discharge interruption switching means as current adjustment means for decreasing the primary current before stopping the primary current flowing through the primary winding after electricity supply is resumed. Thus, unnecessary generation of spark discharge and needless consumption of power can be suppressed.
In general, in an ignition apparatus for an internal combustion engine, the power source voltage output from a power source unit varies at the time of startup of the internal combustion engine or due to improper operation of a generator, resulting in variations in the amount of magnetic-flux energy accumulated in the ignition coil. That is, when the power source voltage output from the power source unit of the internal combustion engine exceeds its rated value, a larger current flows through the primary winding than in an ordinary state, with the result that an excessive amount of magnetic-flux energy is accumulated in the ignition coil.
Therefore, in the ignition apparatus disclosed in Japanese Patent Application Laid-Open No. 11-41717, if an excessive amount of magnetic-flux energy is accumulated in the ignition coil, an excessive amount of magnetic-flux energy remains in the ignition coil when spark discharge is interrupted, and an excessively large current flows through the spark-discharge interruption switching means. Consequently, the load imposed on the spark-discharge interruption switching means increases, and thus the durability of the spark-discharge interruption switching means is lowered. In addition, an excessive amount of electric charge is accumulated within the capacitor serving as a current adjustment means, and in the worst case, the capacitor may be broken. If the current adjustment means breaks, the flow of primary current caused by resumption of electricity supply is interrupted abruptly, so that spark discharge is generated a plurality of times during a single combustion stroke of the internal combustion engine, resulting in accelerated consumption of the spark plug electrodes. In addition, the reliability of the ignition apparatus may be impaired due to the lowered durability of the spark-discharge interruption switching means.
The present invention has been accomplished in view of the above-described problems of the prior art. It is therefore an object of the present invention to provide an ignition apparatus for an internal combustion engine which, without controlling the duration of supply of electricity to the primary winding of an ignition coil before spark discharge, minimizes the amount of spark energy supplied to a spark plug to thereby suppress needless consumption of the spark plug and which can prevent breakage of constituent components, which would otherwise occur due to variation in the amount of magnetic-flux energy accumulated in the ignition coil.
The above-object has been achieved in a first aspect of the invention by providing an ignition apparatus for an internal combustion engine comprising: a DC power source unit; an ignition coil having a primary winding through which primary current flows upon application to the primary winding of power source voltage from the DC power source unit, and a secondary winding which forms a closed loop in cooperation with a spark plug attached to the internal combustion engine; switching means connected in series to the primary winding and adapted to interrupt and resume the primary current flowing through the primary winding; and ignition control means for outputting an ignition command signal for controlling ignition timing, the ignition command signal causing the switching means to interrupt and resume the primary current flowing through the primary winding in order to generate at the secondary winding high voltage for ignition to thereby cause the spark plug to generate spark discharge, wherein the ignition apparatus further comprises: spark-discharge duration time setting means for setting a spark-discharge duration time on the basis of operation conditions of the internal combustion engine, the spark-discharge duration time representing a period during which spark discharge of the spark plug is to be maintained; spark-discharge interruption control means for outputting a spark-discharge interruption command signal for controlling the spark-discharge duration time; a spark-discharge interruption circuit for resuming, after generation of spark discharge by the spark plug, supply of the primary current to the primary winding in accordance with the spark-discharge interruption command signal so as to interrupt the spark discharge; and energy control means for maintaining at a substantially constant level magnetic flux energy which accumulates in the ignition coil by supply of electricity to the primary winding by means of the ignition control means.
In the ignition apparatus for an internal combustion engine according to the present invention having the above-described configuration, the spark-discharge duration time setting means sets, on the basis of operation conditions of the internal combustion engine, a spark-discharge duration time necessary for burning a fuel-air mixture; and the spark-discharge interruption control means controls the spark-discharge interruption command signal in accordance with the spark-discharge duration time. The spark-discharge interruption circuit is operated in accordance with the spark-discharge interruption command signal in order to resume supply of primary current to the primary winding to thereby interrupt spark discharge of the spark plug.
That is, the ignition apparatus for an internal combustion engine according to the present invention interrupts spark discharge by resuming the supply of primary current to the primary winding and thus controls spark energy supplied to the spark plug in accordance with operation conditions of the internal combustion engine. It is noted that when the supply of primary current is resumed during spark discharge, the magnetic flux energy which has been decreasing with consumption of the electromotive force generated at the secondary winding is apt to increase, with the result that the ignition coil generates an electromotive force in a direction which maintains decreasing magnetic flux energy decreasing (i.e., a voltage having a polarity opposite that in effect at the time of spark discharge). Thus, spark discharge is interrupted.
In the ignition apparatus for an internal combustion engine according to the present invention, the period for supplying electricity to the primary winding before spark discharge is set long in order to accumulate sufficient magnetic flux energy in the ignition coil. Therefore, a high voltage can be generated at the secondary winding for ignition which has a magnitude sufficient for generating spark discharge reliably under any operation condition of the internal combustion engine. In addition, since the spark-discharge duration time is controlled in accordance with operation conditions of the internal combustion engine, supply of excessive spark energy to the spark plug can be prevented.
When the internal combustion engine is operated under conditions, such as high-speed, heavy-load conditions, in which only a relatively small amount of spark energy is required, the spark-discharge duration time is shortened in order to cause the spark plug to reliably generate spark discharge through application of high voltage for ignition thereto, while suppressing excessive supply of spark energy to the spark plug to thereby suppress generation of multiple discharge. In contrast, when the internal combustion engine is operated under conditions, such as low-speed, light-load conditions, in which ignition of fuel-air mixture is difficult, the spark-discharge duration time is increased in order to reliably burn the fuel-air mixture. That is, since the spark-discharge duration time is controlled optimally on the basis of operation conditions of the internal combustion engine, generation of multiple discharge and consumption of the spark plug electrodes are suppressed to thereby extend the service life of the spark plug. In addition, occurrence of misfire can be suppressed.
In the ignition apparatus for an internal combustion engine according to the present invention, when spark discharge of the spark plug is to be interrupted, the spark-discharge interruption circuit is operated in accordance with the spark-discharge interruption command signal for controlling the spark-discharge duration time. As described in a second aspect of the invention, the spark-discharge interruption circuit may include an electricity-supply resumption circuit connected in parallel to the switching means adapted to interrupt and resume the primary current flowing through the primary winding. The electricity-supply resumption circuit includes spark-discharge interruption switching means for resuming supply of the primary current to the primary winding in accordance with the spark-discharge interruption command signal; and current adjustment means connected in series to the spark-discharge interruption switching means and adapted to reduce the primary current flowing through the primary winding, after resumption of supply of the primary current to the primary winding, so as to prevent the spark plug from generating spark discharge.
As described above, when spark discharge of the spark plug is to be interrupted, the spark-discharge interruption switching means of the electricity-supply resumption circuit is driven in accordance with the spark-discharge interruption command signal, to thereby resume the supply of electricity to the primary winding. The primary current which flows through the primary winding upon resumption of electricity supply is not interrupted instantaneously, but is decreased gradually by the current adjustment means of the electricity-supply resumption circuit such that the spark plug does not generate spark discharge. That is, after the supply of electricity to the primary winding is resumed so as to interrupt spark discharge of the spark plug, the current adjustment means gradually reduces the primary current which flows upon resumption of electricity supply, to thereby prevent generation of high voltage at the secondary winding when the resumed electricity supply is stopped.
Notably, instead of using the above-described electricity-supply resumption circuit, the spark-discharge interruption circuit may be configured such that a switching element such as a thyristor or a mechanical relay is connected to the opposite ends of the primary winding in parallel thereto, and the opposite ends of the primary winding are short-circuited by means of the switching element.
Further, in the ignition apparatus for an internal combustion engine according to the present invention, the energy control means maintains at a substantially constant level the magnetic flux energy which is accumulated in the ignition coil by virtue of supply of electricity to the primary winding by means of the ignition control means. Therefore, even when the magnetic flux energy accumulated in the ignition coil changes, mainly due to variation in the power source voltage, the magnetic flux energy accumulated in the ignition coil is controlled at a substantially constant level by the energy control means. As a result, the constituent elements, such as spark-discharge interruption switching means, of the spark-discharge interruption circuit are not broken. Also, their durability is not deteriorated, which breakage or durability deterioration would otherwise occur due to accumulation of excess magnetic flux energy in the ignition coil at the time that the spark discharge is interrupted. Therefore, the reliability of the ignition apparatus can be enhanced.
Therefore, in the ignition apparatus for an internal combustion engine according to the first aspect of the present invention, since the spark energy supplied to the spark plug is controlled by interrupting spark discharge performed on the basis of operation conditions of the internal combustion engine, useless consumption of the electrodes of the spark plug can be suppressed. In addition, since excessive magnetic flux energy is not accumulated in the ignition coil at the time of electricity being supplied to the primary winding by means of the ignition control means, problems such as breakage of a constituent element of the spark-discharge interruption circuit for interrupting spark discharge can be prevented. Through combined use of the energy control means and the spark-discharge interruption circuit, which operates in accordance with the spark-discharge interruption command signal, influence of variation in the magnetic flux energy accumulated in the ignition coil is suppressed in order to enable more reliable performance of the operation of interrupting spark discharge of the spark plug on the basis of operation conditions of the internal combustion engine, to thereby improve the reliability of the ignition apparatus.
In the ignition apparatus for an internal combustion engine according to a third aspect of the present invention, the energy control means for maintaining the magnetic flux energy accumulated in the ignition coil at a substantially constant level may include electricity-supply-start timing delay means for detecting power source voltage output from the DC power source unit, for setting, on the basis of the power source voltage, an electricity-supply-start delay time representing a time by which start of supply of electricity to the primary winding is to be delayed, and for delaying by the electricity-supply-start delay time the timing at which the ignition control means starts supply of electricity to the primary winding. That is, in the ignition apparatus for an internal combustion engine according to the present invention, the energy control means is configured such that the supply of electricity to the primary winding is not simply started in response to an ignition command signal which is output in accordance with operation conditions of the internal combustion engine, but the timing for starting supply of electricity to the primary winding before spark discharge is delayed in accordance with the power source voltage output from the DC power source unit.
Such electricity-supply-start timing delay means may be realized by means of a circuit configuration which can maintain the switching means in an OFF state irrespective of control of the ignition command signal by the ignition control means; e.g., a circuit configuration which can change or maintain the ignition command signal input to the switching means in a state which brings the switching means into an OFF state. Until the electricity-supply-start delay time has elapsed after an ignition command signal is output from the ignition control means in order to bring the switching means into an ON state, the electricity-supply-start timing delay means forcedly changes the state of the ignition command signal such that the switching means comes into an OFF state. Thus, the ignition command signal whose state has been changed by the electricity-supply-start timing delay means is input to the switching means, and consequently the ignition control means becomes unable to control the switching means. As result, supply of electricity to the primary winding is not started at the electricity-supply-start timing instructed by the ignition control means.
When the electricity-supply-start timing delay means stops the forced control of the ignition command signal input to the switching means after elapse of the electricity-supply-start delay time, the ignition control means becomes able to control the switching means, and thus, the switching means comes into an ON state by virtue of control by the ignition control means. As a result, supply of electricity to the primary winding is started. The above-described operation enables delay of the timing of starting the supply of electricity until the electricity-supply-start delay time elapses from the electricity-supply-start timing determined by the ignition control means.
Since the electricity-supply-start timing delay means sets the electricity-supply-start delay time in accordance with the power source voltage, even when the power source voltage varies, the magnetic flux energy accumulated in the ignition coil can be maintained at a substantially constant level.
Notably, the electricity-supply-start delay time is preferably set such that the electricity-supply-start delay time increases with the power source voltage. Notably, the electricity-supply-start timing delay means controls only timing for starting supply of electricity to the primary winding and does not change the timing of interrupting the primary current (i.e., ignition timing), and the ignition timing is determined by the ignition control means. Therefore, provision of the electricity-supply-start timing delay means exerts no influence on the ignition timing.
Incidentally, the ignition control means is typically realized by means of the internal processing of a main controller (ECU), which is constituted by a microcomputer mainly consisting of a CPU, RAM, ROM and an input/output section. A recent main controller provided on an internal combustion engine controls not only ignition but also many other items, such as fuel injection amount, air-fuel ratio, and fuel injection timing, on the basis of signals input from sensors (e.g., crank angle sensor) provided at different portions of the internal combustion engine. Therefore, the load imposed on the internal processing of the main controller has increased considerably.
Therefore, when the main controller performs, in addition to various existing control processes, a series of processes for interrupting spark discharge and a process for delaying the timing of starting supply of electricity to the primary winding, the processing load may increase, with the result that the main controller becomes unable to perform the various control processes properly.
In particular, in the case of an internal combustion engine having a large number of cylinders, since the number of control processes to be performed individually for each cylinder increases, the processing load increases further.
When the above-described ignition apparatus of the third aspect of the invention is used for an internal combustion engine having a plurality of cylinders, as described in a fourth aspect of the invention, the ignition coil, the switching means, and the spark-discharge interruption circuit are provided for each of the spark plugs attached to the respective cylinders. The ignition control means comprises a main controller including the spark-discharge duration time setting means; and a signal processing unit including the electricity-supply-start timing delay means and the spark-discharge interruption control means. The main controller sets an ignition timing and a spark-discharge duration time for each cylinder on the basis of operation conditions of the internal combustion engine, and generates a reference ignition command signal corresponding to the ignition timing. The signal processing unit receives the reference ignition command signal output from the main controller and outputs to the switching means an ignition command signal which is delayed from the reference ignition command signal by the electricity-supply-start delay time, and generates, on the basis of the spark-discharge duration time set by the main controller, a spark-discharge interruption command signal to be output to the spark-discharge interruption circuit.
That is, the processing for generating the reference ignition command signal on the basis of operation conditions of the internal combustion engine is performed in the main controller; and the processing for controlling the ignition command signal which is output to the switching means on the basis of the reference ignition command signal is performed in the signal processing unit. Thus, the processing necessary for generation of spark discharge is effected in order to generate spark discharge.
Further, the processing for setting the spark-discharge duration time is performed in the main controller; and the processing for controlling the spark-discharge interruption circuit is performed in the signal processing unit. Thus, the processing for interrupting spark discharge is performed in order to control energy supplied to the spark plug.
Since the processing for generating spark discharge and the processing for interrupting spark discharge are executed while being distributed between the main controller and the signal processing unit, an increase in the processing load of the main controller is suppressed.
Moreover, the processing for delaying the timing of starting the supply of electricity to the primary winding in accordance with variation of the power source voltage is performed in the signal processing unit in order to maintain at a substantially constant level the magnetic flux energy accumulated in the ignition coil. This protects the constituent elements of the spark-discharge interruption circuit, while suppressing an increase in the processing load of the main controller.
Therefore, in the fourth aspect of the present invention, since the processing for generating spark discharge and the processing for interrupting spark discharge are executed while being distributed between the main controller and the signal processing unit, an increase in the processing load of the main controller is suppressed, and various types of control processing can be executed properly in the main controller.
Notably, in order to delay the timing of starting the supply of primary current, the signal processing unit may include a signal path for outputting the reference ignition command signal directly to the switching means as an ignition command signal; and signal interruption means for breaking or disconnecting, if necessary, the signal path for outputting the reference ignition command signal directly to the switching means. That is, when the signal path is broken or disconnected by means of the signal interruption means, the ignition command signal is not output in accordance with the reference ignition command signal. The signal path is connected again upon elapse of the electricity-supply-start delay time from the time at which the supply of electricity is instructed by the reference ignition command signal. Thus, the timing of starting the supply of electricity to the primary winding can be delayed.
If such a signal processing unit is employed, even when the signal processing unit does not operate properly due to a certain cause, the signal path is maintained in a connected state; consequently, the switching means can be controlled directly in accordance with the reference ignition command signal from the main controller. Therefore, at least generation of spark discharge can be effected in order to continue the operation of the internal combustion engine.
When processing is executed while being distributed between the main controller and the signal processing unit, wire lines (signal paths) for sending the reference ignition command signal and the spark-discharge duration time from the main controller to the signal processing unit must be provided. However, in order to increase the packaging efficiencies of the main controller and the signal processing unit, the number of input terminals or output terminals is desirably decreased in order to reduce occupation areas.
In view of the foregoing, a configuration as described in a fifth aspect of the invention is preferably employed in order to communicate to the signal processing unit the spark-discharge duration time set by the main controller. That is, in order to communicate to the signal processing unit the spark-discharge duration time set by the spark-discharge duration time setting means, while maintaining the form of a portion of the reference ignition command signal used to communicate an ignition timing, the main controller changes the form of another portion of the reference ignition command signal in order to include information representing the spark-discharge duration time; and the signal processing unit reads the spark-discharge duration time from the reference ignition command signal output from the main controller and generates the spark-discharge interruption command signal on the basis of the spark-discharge duration time.
That is, only a signal path for sending a reference ignition command signal is provided between the main controller and the signal processing unit; and the form of the reference ignition command signal is changed in order to include information representing the spark-discharge duration time, to thereby communicate from the main controller to the signal processing unit the spark-discharge duration time, as well as the ignition timing. Since the form of the portion of the reference ignition command signal used for communicating an ignition timing is maintained, even when the form of reference ignition command signal is changed in order to communicate the spark-discharge duration time, an erroneous ignition timing is not communicated to the signal processing unit.
Since provision of a wiring line for communicating the spark-discharge duration time between the main controller and the signal processing unit is not required, the number of input or output terminals can be reduced in order to simplify the structure of the ignition apparatus.
In the case in which the reference ignition command signal is output as a pulse signal which represents an ignition timing and a primary-current supply period before spark discharge, the form of the reference ignition command signal is preferably changed such that the pulse width of the pulse signal is changed so as to communicate the spark-discharge duration time. That is, the spark-discharge duration time is communicated from the main controller to the signal processing unit by use of a notification reference ignition command signal having a pulse width different from that of the ordinary reference ignition command signal.
A rule for defining the relationship between the spark-discharge duration time and the number of continuously-output notification reference ignition command signals or the relationship between the spark-discharge duration time and the pulse width of a notification reference ignition command signal is determined in advance; and the main controller communicates the spark-discharge duration time to the signal processing unit by use of the notification reference ignition command signal(s) and in accordance with the rule.
In the signal processing unit, the spark-discharge interruption control means detects the spark-discharge duration time from the number of continuously-output notification reference ignition command signals or the pulse width of the notification reference ignition command signal. Subsequently, the spark-discharge interruption control means interrupts spark discharge when the spark-discharge duration time has elapsed after generation of spark discharge.
Therefore, the ignition apparatus for an internal combustion engine according to a fifth aspect of the present invention eliminates the necessity of providing a wiring line between the main controller and the signal processing unit in order to communicate the spark-discharge duration time only. Thus, the structure of the ignition apparatus can be simplified, and packaging efficiency can be improved.
Since the pulse width of the notification reference ignition command signal corresponds to the primary-current supply period before spark discharge, generation of spark discharge may become difficult if the pulse width of the notification reference ignition command signal is excessively narrow. Therefore, the pulse width of the notification reference ignition command signal is preferably set wider than the narrowest pulse width necessary for generation of spark discharge.
Incidentally, in the case of an internal combustion engine having a plurality of cylinders, pistons accommodated in the respective cylinders are connected to a common crank shaft and cause reciprocating motion, and therefore, the sequence of spark-discharge generation timings (i.e., ignition timings) of the respective cylinders is constant. Since the sequence of ignition timings of the plurality of cylinders is fixed, the internal combustion engine can be operated when the spark plugs provided for the respective cylinders are caused to generate spark discharge in a predetermined sequence, one spark plug at a time, every time a signal representing the ignition timings of all the cylinders is output after detection of the ignition timing of a certain cylinder.
In view of the above, as described in a sixth aspect of the invention, the signal processing unit of the ignition apparatus provided for an internal combustion engine having a plurality of cylinder preferably comprises: signal processing control means for executing at least the processing of the spark-discharge interruption control means and the processing of the electricity-supply-start timing delay means; a first signal path for supplying to the signal processing control means at least one of the reference ignition command signals for the respective cylinders output from the main controller; and a second signal path for supplying to the signal processing control means a synthesized ignition command signal obtained through synthesis of all the reference ignition command signals output from the main controller, wherein the signal processing control means uses, as a reference, a time at which the reference ignition command signal is input from the first signal path, and outputs ignition command signals for the respective cylinders in a predetermined sequence such that one ignition command signal is output every time the synthesized ignition command signal is input from the second signal path.
That is, the signal processing control means of the signal processing unit receives, via the first signal path, a reference ignition command signal used for identifying the ignition timing of a certain cylinder, and receives, via the second signal path, a synthesized ignition command signal which represents the ignition timings of all the cylinders.
Therefore, the signal processing control means can use, as a reference, the reference ignition command signal for the predetermined single cylinder, and output ignition command signals for the respective cylinders in a predetermined sequence such that one ignition command signal is output every time the synthesized ignition command signal is input. Thus, spark discharge can be generated at a proper timing in each cylinder to thereby operate the internal combustion engine.
Since inputting all the reference ignition command signals to the signal processing unit becomes unnecessary, in the case of an internal combustion engine having three or more cylinders, ignition command signals for the respective cylinders can be output at proper timings even when the number of input terminals of the signal processing control means; i.e., the number of input terminals for inputting the reference ignition command signals, is less than the number of the cylinders of the internal combustion engine.
Therefore, the ignition apparatus for an internal combustion engine according to the sixth aspect of the present invention can reduce the number of input terminals of the signal processing control means provided in the signal processing unit, to thereby increase the packaging density of the signal processing control means.
Notably, the synthesized ignition command signal is preferably obtained through logical addition (OR) of all the reference ignition command signals such that the synthesized ignition command signal enters an ON state when at least one of the reference ignition command signals enters an ON state.
Incidentally, the above-described ignition apparatus for an internal combustion engine (any one of the first through sixth aspects of the invention) achieves the effect more remarkably when the ignition apparatus is used for a gas engine using a gaseous fuel as described in a seventh aspect of the invention.
That is, since gaseous fuel has a higher insulating resistance than does liquid fuel (e.g., gasoline), in order to reliably ignite fuel in a gas engine, ignition voltage higher than that for gasoline engines must be generated in order to generate strong spark discharge. Accordingly, an ignition coil for a gas engine using a gaseous fuel must be designed such that the ignition coil generates a maximum secondary voltage (high voltage for ignition) higher than that for gasoline engines (e.g., whereas the maximum secondary voltage of an ignition coil for a gasoline engine is 30 kV or higher, the maximum secondary voltage of an ignition coil for a gasoline engine is 40 kV or higher).
Therefore, in the case of a gas engine, the magnitude of current which is intermittently supplied to the primary winding of an ignition coil is set relatively high. Therefore, conceivably, a large amount of unnecessary spark energy may be supplied to the spark plug, to thereby further shorten the service life of the spark plug.
In the case of a gas engine, when the power source voltage increases, the primary current flowing through the primary winding increases further, and the current flowing through a transistor serving as the switching means increases further. In this case, the heat generation of the transistor increases, and the transistor may burn out. Therefore, when the above-described ignition apparatus of the present invention is used for a gas engine in order to maintain the magnetic flux energy accumulated in the ignition coil at a substantially constant level, excessive current does not flow through the transistor over a long period of time, whereby excessive heat generation of the transistor serving as the switching means can be prevented.
In the case in which the ignition apparatus according to any one of the first through sixth aspects of the invention is applied to a gas engine as described in the seventh aspect of the invention, an effect of preventing excessive heat generation of the switching means due to variation in the magnetic flux energy accumulated in the ignition coil can be obtained.
In some ignition apparatuses used for stationary gas engines, AC voltage (e.g., 100 or 200 V) supplied from a commercial power source such as an electric power company is converted to DC voltage by use of a transformer, a rectifier, a smoothing circuit, etc.; and the thus-obtained DC voltage is used to generate current to be supplied to the primary winding, to thereby generate high voltage for ignition.
In the case of an ignition apparatus used for a stationary gas engine which uses a commercial power source, voltage applied to the primary winding of the ignition coil is apt to change, with the possible result that the switching means generates excessive heat and bums out. That is, the demand for electric power supplied from an electric power company changes seasonally, and the magnitude of the AC voltage supplied from the commercial power source changes due to variation in the demand for power among seasons (e.g., between summer and winter). Notably, the AC voltage supplied from the commercial power source changes within a predetermined tolerance range.
Since the AC voltage supplied from the commercial power source such as an electric power company changes within the tolerance range, the magnitude of DC voltage obtained from the AC voltage also changes seasonally. Therefore, in the case of a stationary gas engine, the power source voltage used for generating current to be supplied to the primary winding changes seasonally.
As described above, in the case of a gas engine, since the period for supplying primary current is determined in consideration of a case in which the ignitability of fuel is at its poorest level, the period for supplying primary current is determined on the basis of the magnitude of DC voltage in a season in which the magnitude of DC voltage becomes lowest (i.e., primary current becomes smallest). In this case, during seasons in which the magnitude of DC voltage increases, the primary current becomes excessive even when the primary-current supply period is controlled properly, thereby increasing the possibility of the switching means generating excessive heat.
Accordingly, when the above-described ignition apparatus is applied to a stationary gas engine, the effects of the present invention can be achieved more remarkably. That is, since the magnetic flux energy accumulated in the ignition coil is maintained at a substantially constant level, it is possible to prevent excessive current from flowing through a transistor for a long period, to thereby protect the switching means.